AE Aquarii
First white dwarf known to emit pulsar-like pulsations.
AE Aquarii is a binary star system classified as a cataclysmic variable of the DQ Herculis type. Parallax measurements place it roughly 280 light-years (86 parsecs) from Earth. The system is notable for its white dwarf, which is the first of its kind known to produce pulsar-like pulses driven by its rotation and the acceleration of particles.
The star’s variability was first noted by Arno Arthur Wachmann, who examined four photographic plates taken between 1923 and 1930. Based on this limited data, he initially classified it as a Mira variable and published the discovery in 1931 under the designation 342.1931 Aquarii. In 1938, Ernst Zinner reclassified it as a cataclysmic variable after studying a much larger set of observations; by then it had received the variable star designation AE Aquarii.
The system comprises an ordinary star in a tight orbit around a magnetic white dwarf, with an orbital period of 9.88 hours. The white dwarf has 63% of the Sun’s mass but only about 1% of its radius. As of 2009, it holds the record for the shortest known spin period of any white dwarf, completing one rotation every 33.08 seconds. This spin is slowing at an unusually high rate of 1.78 nanoseconds per year. The secondary star is a K4-5 V main-sequence star, fusing hydrogen in its core. It has about 37% of the Sun’s mass and 79% of its radius.
Flare activity has been observed across multiple wavelengths, including X-rays. Most of the mass lost from the secondary star is ejected from the system by the rapidly spinning magnetic white dwarf. The X-ray luminosity likely results from mass accreting onto the white dwarf at an estimated rate of about 7.3 × 10¹⁰ kilograms per second.
- Distance
- about 280 light-years (86 parsecs)
- Orbital period
- 9.88 hours
- White dwarf mass
- 63% of the Sun's mass
- White dwarf radius
- about 1% of the Sun's radius
- White dwarf spin period
- 33.08 seconds
- Spin period decrease rate
- 1.78 ns per year
- Secondary star class
- K4-5 V
- Secondary star mass
- about 37% of the Sun's mass
- Secondary star radius
- 79% of the Sun's radius
- Accretion rate
- about 7.3 × 10^10 kg per second
Lore & Background
Arno Arthur Wachmann discovered that the star was variable after examining four photographic plates taken from 1923 through 1930. He classified the star as a mira variable based on that sparse data set. Wachmann published the discovery in 1931, naming the star 342.1931 Aquarii. In 1938, Ernst Zinner classified the star, which by then had received the variable star designation AE Aquarii, as a cataclysmic variable, based upon a much larger data set.
The AE Aquarii system consists of an ordinary star in a close orbit around a magnetic white dwarf; the pair orbit each other with a period of 9.88 hours. The white dwarf primary has 63% of the Sun's mass but a radius of only about 1% of the Sun. As of 2009, it has the shortest known spin period of any white dwarf, completing a full revolution every 33.08 seconds. This spin is decreasing at a rate of 1.78 ns per year, which is unusually high. The secondary star has a stellar classification of K4-5 V, making it a main sequence star that is generating energy at its core through the thermonuclear fusion of hydrogen. It has about 37% of the Sun's mass but 79% of the Sun's radius.
This system displays flare activity that has been observed across multiple bands of the electromagnetic spectrum, including X-rays. Mass is being lost from the secondary star, most of which is being flung out of the system by the rapidly spinning magnetic primary. The X-ray luminosity is likely being caused by the accretion of mass onto the white dwarf, which is occurring at an estimated rate of about 7.3 × 10^10 kg per second.
Reader's Guide
AE Aquarii holds significance as the first white dwarf known to produce pulsar-like pulsations powered by its rotation and particle acceleration, a unique property that has made it the subject of numerous scientific studies. Its white dwarf has the shortest known spin period of any white dwarf as of 2009, at 33.08 seconds, with an unusually high spin-down rate of 1.78 ns per year. The system's flare activity across multiple electromagnetic bands, including X-rays, and the estimated accretion rate of about 7.3 × 10^10 kg per second onto the white dwarf contribute to its importance in understanding cataclysmic variables and magnetic white dwarf behavior. The discovery history, from Wachmann's initial misclassification as a mira variable in 1931 to Zinner's correct reclassification as a cataclysmic variable in 1938, illustrates the refinement of observational data. The system's legacy includes its role as a benchmark for studying accretion processes, magnetic fields, and rotation-powered emission in white dwarfs, with comparisons drawn to pulsars and X-ray pulsars.
Did You Know?
- AE Aquarii is the first white dwarf known to emit pulsar-like pulsations powered by its rotation and particle acceleration.
- The white dwarf in AE Aquarii has the shortest known spin period of any white dwarf, at 33.08 seconds as of 2009.
- The system's spin period is decreasing at an unusually high rate of 1.78 ns per year.
- Arno Arthur Wachmann originally classified AE Aquarii as a mira variable in 1931, but Ernst Zinner reclassified it as a cataclysmic variable in 1938.
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